Answer
$C_2H_4(g)+3O_2(g)\rightarrow 2CO_2(g)+2H_2O(g)$
This is combustion.
Work Step by Step
$C_2H_4(g)+O_2(g)\rightarrow CO_2(g)+H_2O(g)$
A reaction with oxygen is combustion.
Add a coefficient of 2 to $CO_2$ to balance $C$.
Add a coefficient of 2 to $H_2O$ to balance $H$.
$C_2H_4(g)+O_2(g)\rightarrow 2CO_2(g)+2H_2O(g)$
Add a coefficient of 3 to $O_2$ to balance $O$.
$C_2H_4(g)+3O_2(g)\rightarrow 2CO_2(g)+2H_2O(g)$
